It is clearly desirable, then, that video cassettes should be provided with some kind of play-counting device. One proposal was the so-called "R-Cassette" developed in the U.S.A. in 1981. This enables a video cassette intended for rental to lock automatically after one viewing. The cassette can only be rewound by using a special device, supplied only to dealers, which is linked up to a central computer that records each "use", thus enabling an exact calculation to be made of the number of times the video has been hired. This system would also enable payments to be made to copyright owners, calculated on a per rental basis. Among the factors that make this system unacceptable are:
1. It frustrates those renters who wish to view all or part of a program more than once.
2. It loads onto the dealer the time wasting task of rewinding every tape after rental.
3. It does not uniquely identify cassettes and so permits the continued depredations of pirates.
4. It requires dealers to invest in equipment that is otherwise irrelevant to the operation of his business.
The other system is known as the "Screen Key Card" system and operates by recording the material to be rented on cassette in a scrambled form. Customers are issued with a card containing a de-scrambling code which must be used in order to gain access to the video tape. This card also contains coded details of the subscriber's name, address, etc, thus enabling identification, invoicing and payment for each rental use. Each time the customer rents, the relevant de-scrambling code is programmed into the card and each time the de-scrambler is activated an electronic mark is made on the de-scrambled material. This system, however, requires the acquisition of special and complex hardware by every renter and appears to offer no auditing capability to the distributor.
Other proposals for counting and displaying the number of plays of a cassette have been proposed, but none has proven successful.
U.S. Pat. No. 3,995,319 discloses an audio tape cassette having a mechanical counter actuated by a geared arm in one corner of the cassette, the counter arm having a stop which stops the arm at an integral count so that the arm stands clear of the tape wound on the spool. This system has problems rendering it impractical. In particular the angle of the sensing arm in relation to the tape is likely to cause jamming, and uneven tension on the tape results from the fact that the arm, at times, stands clear of the tape and, at times, rubs against the tape. The space in the corner of a cassette is too restricted for location of an inexpensive and reliable counter mechanism. Furthermore, the movement of the tape reels inside the cassette when it is shaken would make such a device subject to false indexing.
U.S. Pat. No. 4,466,584 discloses video cassette having an escapement driven counter, actuated by a rocking member having two feeler arms in the free space between the spools, one riding on the tape wound on each spool. While this arrangement avoids the problem of the restricted space in the corner of a video cassette which prevents the use of the device disclosed in U.S. Pat. No. 3,995,319 on video tape cassettes, the escapement drive is complicated, and reliance on the wedging action between the tooth of the rocking member as it is radially driven into the toothed wheel to provide the wedging force to move the toothed wheel is unreliable. Furthermore, because the radius of the tape spools does not change linearly as the tape is played, at times, enough free space may be left between the arms and the spools to permit shaking of the cassette alone to falsely register a count (or to subtract a count). Also, the problem of uneven tension on the tape is still present since the arms are not continuously urged against the tape. Still further, the counting mechanism disclosed in U.S. Pat. No. 4,466,584 interferes with the spool brake, typically present in video tapes, because all space is taken up by the rocking member and escapement mechanism.